The air compressor on heavy-duty trucks and off-road equipment is constantly in operation. To shut the compressor down, i.e. to stop generating air, the compressor is designed to vent the discharge of the compressor to the atmosphere. Typically a governor that regulates the air pressure in the system will send a signal to open a valve, resulting in a venting of the system and a release of air pressure.
The invention of the integrated compressor high-pressure protection valve is the result of a need to protect the compressor, and other system components, from unintentional high pressure in the air system in the case of a failure in the venting process in normal operation.
Through unforeseen failures, the compressor may stay in the loaded, or on-cycle, condition, and keep building up the air pressure in the air brake system to the point of failure of some components. There are documented failures within the industry where the air compressor had failed to shut down, causing several hundreds to thousands of dollars of repairs and lost time. Commonly, high pressure relief valves are located down-stream in the air system and not in the head of the compressor. While generally providing emergency relief for the entire system, these down stream high-pressure relief valves are more effective in protecting the components in the system which are proximate to the relief valves. However, failures often occur in the winter months, where moisture can collect and freeze, which isolates down-stream high-pressure relief valves from the air compressor. In this case, if a high-pressure situation is encountered, the relief valve may not relieve the pressure at the air compressor, and the air compressor may be damaged.
It is well known to utilize valves of different designs in air compressor systems to individually perform either an unloading/venting function or a high pressure relief function. Current compressors, however, used in the heavy trucking industry do not incorporate high pressure relief with unloading of the compressor. Typically, a separate high pressure relief valve is required in the air system, and is installed at various locations within that system. Usually, these are not available to protect the compressor, but to protect those devices that are near to them.
Similarly, current compressors that do have a high pressure relief valve incorporated into the head of an air compressor have been single function only. These compressors do not couple this feature to a valve device that will also unload the compressor. While it is known to incorporate numerous sub-valves within complex multifunction units, these valves do not enjoy the benefits of ease and efficiency in manufacturing, installation and maintenance derived from the single valve performing two necessary functions that can be conveniently assembled in the head of air compressor disclosed herein
An explanation of the use of high pressure relief valves in air brake systems is found in U.S. Pat. No. 3,862,782 to Horowitz et al. Horowitz discloses a control valve for use in a vehicle air brake system to apply brake releasing pressure to spring-actuated brakes. The valve includes a protection valve for the vehicle service tank, as well as a check valve for protecting the vehicle emergency tank. In addition, the valve includes a piston and a shuttle for controlling the passage between the vehicle emergency tank and the spring brake chambers and a check valve for bleeding trapped pressure from the service line.
Also of interest to this disclosure is U.S. Pat. No. 4,907,842 to Goldfein. Goldfein discloses an air brake system with a multifunction control valve; a multifunction control valve for an air brake system; various sub-valves within the multifunction control valve—including a pressure protection valve, a pressure reducing valve, an emergency control valve, and a syncro valve. In one embodiment all four types of sub-valves are within a single unitary housing of the multifunction valve.
The Goldfein patent discloses a pressure reducing valve system for use with a separate compressor for reducing the pressure within an air brake system. However, the Goldfein patent does not disclose a system that further acts as a safety release valve as described in the present invention. Rather, even where the sub-valves are within a single unitary housing of the multifunction valve, Goldfein relies upon a separate pressure protection valve that is unassociated with the pressure reducing valve. Furthermore, the Goldfein patent does not appear to disclose integrating either of these valves into the compressor. Neither the protection relief valve combination nor the integration of such with the compressor is disclosed in Goldfein.
Such a complex setup as disclosed in Goldfein, having numerous sub-valves housed within a multifunction unit, does not enjoy the benefits of ease and efficiency in manufacturing, installation and maintenance derived from the single valve performing two necessary functions that can be conveniently assembled in the head of air compressor disclosed herein.
What is desired therefore is an unloading/venting valve for an air compressor which incorporates high pressure protection with the ability to unload the compressor, which is assembled in the head of the air compressor, which provides easy assembly because it is installed in one set up of the compressor head in the assembly fixture, which protects the compressor from a failure instead of or in addition to protecting associated components in the air system, and which has a high pressure relief valve cannot fail due to it being isolated from the air system.